1. Field of the Invention
This invention relates to a control device for an electric motor for a displaceable motor vehicle part, with a switch unit for controlling the motor, a ratchet wheel which, when the motor vehicle part is displaced, is forced to rotate less than 360 degrees between its end positions via an eccentric gearing and actuates the switch unit depending on the rotary position of the ratchet wheel, the eccentric gearing having an externally toothed internal wheel and an internally toothed external wheel which is interdigitally engaged to it, the ratchet wheel being supported for wobble motion with reference to a motor-driven shaft is coupled to move with movement the displaceable motor vehicle part and which is pivotally mounted in a gearing housing, the ratchet wheel forming either the internal wheel or the external wheel of the eccentric gearing, and the external wheel, the ratchet wheel and the switch unit being located within the gearing housing, and the displaceable motor vehicle part preferably being a cover or a corresponding component of an openable motor vehicle roof.
2. Description of Related Art
A control device of the general type to which the invention is directed is known from German Patent DE 42 09 652 C1, the shaft being joined to rotate with rotation of a worm wheel which is driven by a worm shaft and which is provided with an eccentric recess in which a ratchet wheel is pivotally mounted with respect to the worm wheel, and thus, relative to the shaft. The ratchet wheel forms the internally toothed external wheel of the eccentric gearing. The externally toothed internal wheel of the eccentric gearing is formed on the housing cover. The switch unit is made as a switch with an actuating plunger which adjoins the outside periphery of the ratchet wheel in order to actuate the switch depending on the rotary position of the ratchet wheel. The outside periphery of the ratchet wheel is thus made essentially undulatory in order to compensate for the wobbling of the ratchet wheel. In a certain angular range, the outside periphery is provided with a trip cam in order to actuate the switch of the switch unit by means of the actuating plunger.
The disadvantage in this known control device is that the device requires a relatively large amount of space in the radial direction due to the switch which is provided on the outside periphery of the ratchet wheel and thus cannot be built to be especially compact.
Published German Patent Application DE 40 38 284 A1 discloses a control device for a window opener in which a disk which is to rotate with the drive motor of the window opener is magnetically coded so that its rotary position can be acquired by a Hall element. Instead of the Hall element, an optoelectronic, capacitive, inductive or ohmic scanning element can be used.
German Patent DE 38 29 405 C2 discloses a drive device for a sliding roof in which a gear wheel is provided with a magnetic ring which is driven by single-tooth gearing which for its part is driven by a shaft which is driven by the motor. The magnetic ring comprises two segments which are magnetized on opposite poles and is scanned by a magnetic sensor in order to acquire the position of the sliding cover which is driven by the motor-driven shaft.
The primary object of this invention is to devise a control device for an electric motor for a displaceable motor vehicle part which is built as compactly and simply as possible.
This object is achieved as in accordance with the invention by a control device in which a ratchet wheel and a switch unit are made for contactless actuation of the switch unit.
In this approach according to the invention it is advantageous that the control device, on the one hand, makes do with as few parts as possible, and on the other hand, the required construction space can be kept small.
In another advantageous embodiment, the external wheel is made on the gearing housing and the internal wheel is formed by the ratchet wheel. This facilitates a compact and stable construction.
Preferably, the ratchet wheel and the switch unit are made for inductive actuation of the switch unit, the ratchet wheel preferably having a magnetization which changes in the peripheral direction and the switch unit having a Hall sensor which detects the magnetization of the ratchet wheel.
Preferably, the switch unit comprises control electronics implemented on a board which carries the Hall sensor as well and which lies essentially parallel to the ratchet wheel. This enables especially compact execution of the control device.
In one preferred embodiment, the shaft has an eccentric section with respect to which the ratchet wheel can be turned. The shaft is preferably driven via a step-down gearing which is formed by a worm shaft which is connected to the motor, and a worm wheel which interdigitally engages it and sits securely on the shaft. Here, the eccentric section is made preferably in one piece with the worm wheel, and the eccentric section can be injection molded onto the worm wheel. In this way, the number of required mechanical parts can be minimized.
Preferably, the external wheel is made on the inside of a cover section of the gearing housing.
These and further objects, features and advantages of the present invention will become apparent from the following description when taken in connection with the accompanying drawings which, for purposes of illustration only, show several embodiments in accordance with the present invention.